BACKGROUND: Acacetin (5,7-dihydroxy-40-methoxyflavone), present in safflower seeds, plants, flowers, Cirisium rhinoceros Nakai, has been reported to be able to exert anti-peroxidative, anti-inflammatory, anti-plasmodial, and anti-proliferative activities by inducing apoptosis and blocking the progression of cell cycles.
OBJECTIVE AND DESIGN: The objective of this study is to investigate the mechanism of acacetin-induced apoptosis of oral squamous cell carcinoma cell line (HSC-3).
RESULTS: Acacetin caused 50% growth inhibition (IC50) of HSC-3 cells at 25μg/mL over 24h in the MTT assay. Apoptosis was characterized by DNA fragmentation and increase of sub-G1 cells and involved activation of caspase-3 and PARP (poly-ADP-ribose polymerase). Maximum caspase-3 activity was observed with 100μg/mL of acacetin for 24h. Caspase-8 and -9 activation cascades mediated the activation of caspase-3. Acacetin caused reduction of Bcl-2 expression leading to an increase of the Bax:Bcl-2 ratio. It also caused a loss of mitochondrial membrane potential that induced release of cytochrome c into the cytoplasm. Pretreatment with casapse-3 (Z-DEVD-FMK), -8 (Z-IETD-FMK), and 9 inhibitor (z-LEHD-fmk) inhibited the acacetin-induced loss of mitochondrial membrane potential and release of cytochrome c. The mitogen-activated protein kinases (MAPKs) were activated by acacetin. Moreover, pretreating the cells with each of the caspase inhibitor or MAPKs specific inhibitors apparently inhibited acacetin-induced cytotoxicity of HSC-3 cells.
CONCLUSION: In conclusion, acacetin induce the apoptosis of oral squamous cell carcinoma cell line, which is closely related to its ability to activate the MAPK-mediated signaling pathways with the subsequent induction of a mitochondria- and caspase-dependent mechanism. These results strongly suggest that acacetin might have cancer inhibition and therapeutic potential.